Magnetic shunt device for hall effect applications

ABSTRACT

A magnetic shunt device for use in a Hall effect sensor application wherein the shunt device is positioned and located relative to the Hall effect element and is shaped and dimensioned so as to shield and null the influence of the magnetic field when such field is substantially parallel to the sensitive plane of the Hall effect element. The present shunt device ensures that the null output voltage of the Hall effect element in a particular sensor application is consistent for a large number of such sensors despite misalignment problems and mechanical uncertainties in accurately arranging the magnetic devices that generate the magnetic field relative to the Hall effect element at the null or &#34;no action&#34; position of the sensor. The present device also obviates the requirement to use additional electronic circuitry to adjust the output voltage of the Hall effect element at the null or &#34;no action&#34; position.

TECHNICAL FIELD

This invention relates generally to Hall effect devices and, moreparticularly, to Hall effect transducers and sensors having a magneticshunt device associated therewith to null the magnetic field when themagnetic field is parallel to the sensitive face of the Hall effectdevice.

BACKGROUND ART

If exposed to a magnetic field, a current carrying Hall effect devicetypically produces an output voltage that is proportional to both theelectric current and the sine of the angle between the magnetic fieldand the direction of the current flowing through the Hall effect device.That is, if there is no magnetic field, or if the magnetic field isparallel to the current direction flowing through the Hall effectdevice, in other words, the angle between the magnetic field and thecurrent direction is zero, then the output voltage of the Hall effectdevice is either zero, or some null or quiescent output voltage. For agiven electric current magnitude, the output voltage of the Hall effectdevice reaches its maximum value when the magnetic field isperpendicular (+90° and −90°) to the direction of the current.

In order to avoid reversal of the Hall effect output voltage as themagnetic field varies from −90° to +90° around the Hall effect device,linear Hall effect manufacturers bias the Hall effect output voltagesuch that minimum voltage is obtained when the magnetic field is at −90°and maximum voltage (V) is obtained when the magnetic field is at +90°.Therefore, in this arrangement, in the absence of the magnetic field, orif the magnetic field is parallel to the current direction, that is, theangle between the magnetic field and direction of current is zero, alinear Hall effect device should produce an output voltage at this nullor “no action” position that is about half the voltage output (V/2) ofthe device.

In some linear Hall effect transducer applications, the Hall effectdevice output voltage is varied from its minimum value to its maximumvalue by rotating the magnetic field around the Hall effect device at afixed, optimal distance. In this particular application, no magneticfield, or zero angle between the magnetic field and the direction ofcurrent of the Hall effect device, should produce the exact same outputvoltage. However, if the “at rest” position, or “no action” position, ofthe Hall effect device relative to the rotating magnetic fieldcorresponds to the zero angle position therebetween, it may be difficultto mechanically center the magnetic field so that the angle between themagnetic field and the direction of current through the Hall effectdevice is precisely zero for every linear device produced. To attemptthis mechanical centering procedure is both tedious and costly when alarge number of linear Hall effect devices are to be produced. In orderto circumvent this problem, potentiometers and other devices aretraditionally added to the electronic circuitry associated with the Halleffect device to manually adjust the output voltage of such devices forthe zero angle position.

It is, therefore, desirable to provide an easy way to null the affect ofthe magnetic field in a Hall effect sensor application when the magneticfield is parallel to the sensitive face of the Hall effect device.

It is also desirable to provide a Hall effect device that does notrequire additional electronic circuitry to adjust its output voltage atthe zero angle or null position.

Still further, it is likewise desirable to ensure that the null outputvoltage of the Hall effect device in a particular application isconsistent for a large number of such devices used in the sameapplication despite mechanical uncertainties in accurately arranging themagnet(s) or electromagnet(s) and the Hall effect device at the zeroangle or “no action” position.

Accordingly, the present invention is directed to overcoming one or moreof the problems as set forth above.

DISCLOSURE OF THE INVENTION

In accordance with the teachings of the present invention, oneembodiment of a Hall effect sensor is disclosed wherein a magnetic shuntdevice of appropriate size and dimension is positioned around a Halleffect device to null the magnetic field when this field is parallel tothe sensitive plane of the Hall effect device. This shunt configurationensures a consistent null output voltage for a large sample of similardevices despite mechanical positioning uncertainties and misalignmentproblems which arise during construction and manufacturing relative tothe proper orientation of the magnetic devices that generate themagnetic field and the Hall effect device at the zero angle or “noaction” position.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, reference may bemade to the accompanying drawings in which:

FIG. 1 is a partial perspective view of a Hall effect device used in aparticular Hall effect sensor application wherein a shunt deviceconstructed and positioned in accordance with the teachings of thepresent invention is utilized to null the magnetic field when the fieldis parallel to the sensitive plane of the Hall effect device;

FIG. 2 is a diagram of the output voltage of a Hall effect device versusthe magnetic field orientation (θ), that is, the angle between themagnetic field and the direction of current flowing through the Halleffect device; and

FIG. 3 is a schematic diagram showing one embodiment of a feedbackcontrol circuit for adjusting the output voltage of a Hall effect deviceto compensate for errors.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, numeral 10 in FIG. 1 represents one embodiment of aHall effect sensor application 10 that illustrates the principles of thepresent invention. The Hall effect sensor 10 may be of the type used tosense linear and rotary displacement and/or position in a wide varietyof different environments and applications such as for use in workmachines such as track type tractors, articulated trucks, integratedtool carriers, skid steer loaders, backhoe loaders, material handlingmachines, a wide variety of other mining and earthmoving type equipment,and a wide variety of automotive applications, and non-contactsensor/actuator applications.

The Hall effect sensor 10 illustrated in FIG. 1 includes a Hall effectelement or transducer 12 which is mounted in a housing (not shown) suchthat two magnets 14 and 16 are positioned and located in opposedrelationship to each other at a fixed, optimal radius “r” from the Halleffect element 12. Although cylindrical magnets 14 and 16 having adiameter “d” are illustrated in FIG. 1, it is recognized and anticipatedthat the magnets 14 and 16 can take on any shape and size and that suchmagnetic devices may be replaced with electromagnetic devices.

As illustrated in FIG. 1, the magnets 14 and 16 are positioned andlocated so as to be angularly rotatable about the element 12, eachmagnet 14 and 16 being rotatable approximately 180° as will behereinafter explained. This rotation of the magnets can be accomplishedby attaching the magnets to a rotating wheel, disk, or other rotatabledevice contained within the sensor housing. It is recognized andanticipated that other means for accomplishing this task can likewise beutilized.

As depicted in FIG. 1, the magnets 14 and 16 are positioned and locatedsuch that the angle θ=0°, the angle θ being the angle between themagnetic field generated by the magnets 14 and 16 and the sensitiveplane 13 of the Hall effect element 12. In this regard, the sensitiveplane 13 of Hall effect element 13 may include both the front and rearfaces of the element 12. As positioned and located in FIG. 1, the Halleffect element 12 experiences no magnetic field when the magnets 14 and16 are at the zero angle position (angle θ=0°) since the magnetic fieldsof the two respective magnets cancel each other out at this position. Inthis regard, it is important that the polarity of the respective magnetson each opposite side of the element 12 be opposite to each other sothat the cancellation effect of the magnetic fields will occur. Also, atthis particular magnetic orientation, that is, where the angle θ=0°, themagnetic field generated by each respective magnet 14 and 16 is parallelto the direction of current flowing through the Hall effect element 12.

As the orientation of the magnets 14 and 16 rotate around the Halleffect element 12 at the constant radius “r”, a sinusoidal outputvoltage from the element 12 is obtained as best shown in FIG. 2. Theoutput voltage of the Hall element 12 is biased by appropriateelectronics such that minimum voltage is obtained when the magneticfield is at θ=−90° and maximum voltage is obtained when the magneticfield is at θ=+90°. Also, as can be easily seen from FIG. 2, the outputvoltage of the Hall effect element 12 at the orientation illustrated inFIG. 1, that is, where θ=0°, is approximately one-half of the outputvoltage (V/2) of the element 12. Depending upon the particular Halleffect device 12 being utilized, this output voltage is typically a lowlevel signal on the order on 30 microvolts in the presence of a onegauss magnetic field. The bias associated with the Hall effect element12 appears on the output voltage when no magnetic field is present(θ=0°) and is referred to as the null voltage. The Hall effect sensor 10as illustrated in FIG. 1 therefore provides a voltage output that isproportional to the applied magnetic field and such sensor has aquiescent or zero angle output voltage that is approximately 50% of thesupply voltage.

Since it is important that the null output voltage be the same for everyHall effect sensor 10 constructed, it is important that the mechanicalorientation of the magnets or other magnetic devices 14 and 16 relativeto the Hall effect element 12 at the angle θ=0° always be the same sothat the same null voltage is obtained. Since it is difficult tomanufacture a large number of sensors 10 that are always mechanicallyoriented and centered at the θ=0° position, some means must be providedto offset any voltage at this null position that may be due tomisalignment in the positioning and orientation of the various magneticdevices 14 and 16 relative to the Hall effect element 12.

In accordance with the teachings of the present invention, a magneticshunt device 18 is provided that shunts or shields the magnetic fieldgenerated by the magnets 14 and 16 from the Hall effect element 12 whenthe magnetic devices are located at the θ=0° position as illustrated inFIG. 1. The shunt device 18 can take on any particular shape orconfiguration, such as the U-shaped configuration illustrated in FIG. 1,so as to be compatible with the particular sensor configuration involvedso long as the device 18 shields the sensitive plane 13 of the Halleffect element 12 from the magnetic field generated by the magneticdevices at the angle θ=0° position.

In the particular embodiment disclosed in FIG. 1, the magnetic shuntdevice 18 is positioned and located around the Hall effect element 12such that the shunt side portions 20 are disposed in the path of themagnetic field when the magnets 14 and 16 are located at the θ=0°position to shield the sensitive plane 13 from the affects or influenceof the magnetic field flux generated by the magnets 14 and 16 at theθ=0° position. In this regard, the width “c” of the respective shuntside portions 20 relative to the width “a” of the side portions 15associated with the element 12 should be such that both the fore and aftfaces of the sensitive plane 13 of the element 12 are shielded from theinfluence of the magnetic field at the θ=0° position, but that suchsensitive faces are exposed to the affects or influence of the magneticfield at some angular displacement away from the angle θ=0°. Therelationship between the width “c” of the shunt side portions 20 and thewidth “a” of the Hall effect element side portions 15 will determine atwhat angular orientation the sensitive plane 13 of the Hall effectelement 12 will begin to be influenced by the magnetic field.

With the shunt device 18 positioned as illustrated in FIG. 1 around theHall effect element 12, and with the magnets 14 and 16 positioned andlocated at the θ=0° angle, the null voltage output of the element 12will remain consistent for any plurality of sensors 10 even if thealignment of the magnets 14 and 16 relative to the Hall effect element12 at the θ=0° position varies from one sensor to another. The shuntdevice 18 can be constructed from any suitable magnetic material so longas the magnetic properties of such material are such that the magneticfield flex lines are either repulsed by or attracted to the shunt 18 andaround the sensitive plane of the element 12.

As illustrated in FIG. 1, the diameter or width of the respectivemagnets 14 and 16 has been designated the dimension ″d. Although themagnets 14 and 16 are shown as being cylindrical in shape, it isrecognized and anticipated that such magnets could be square,rectangular or some other shape. With this in mind, the dimension “d” isintended to refer to the greatest width associated with the magneticdevices 14 and 16. Since, in general, the magnet width “d” is normallygreater than the width “a” associated with the Hall effect element sideportions 15, in order to null the magnetic field generated by themagnets 14 and 16 when such magnets are located at the position θ=0°,the width “c” of the shunt side portions 20 should be greater than thewidth “a” of the Hall effect element side portions 15. The amount bywhich the width “c” is greater than the width “a” will determine theangular displacement or orientation of the magnetic field relative tothe sensitive plane 13 of the Hall effect element 12 whereby the element12 will again be influenced by the magnetic field. In this regard, thewidth “c” should be no greater than the width or diameter “d” of themagnets 14 and 16 in order to avoid any degradation to the sensingcapabilities of the element 12. As a result, the following relationshipsshould exist between the widths “a” and “c” and the magnet width orradius “d”:

“c”>“a”

“c”<“d”

A good rule of thumb would be to use the equation

“c”=0.9 ×d.

Use of the magnetic shunt device 18 as illustrated in the embodimentdisclosed in FIG. 1 would therefore ensure that any misalignment of themagnets 14 and 16 relative to the sensitive plane of the Hall effectelement 12 at the θ=0° position will have no affect on the null outputvoltage of the element 12 at the “at rest” or “no action” position ofthe sensor 10, that is, at the θ=0° position.

INDUSTRIAL APPLICABILITY

As described herein, the present shunt device 18 has particular utilityin a wide variety of different types of Hall effect sensor applicationssuch as sensing linear or rotary position or displacement. Regardless ofthe particular application, use of the present shunt device 18 willensure a consistent null output voltage from the Hall effect elementdespite mechanical uncertainties in the positioning and orientation ofthe magnetic devices relative to the Hall effect element at the “median”or “no action” position (θ=0°).

In the particular sensor embodiment illustrated in FIG. 1, as themagnets 14 and 16 are angularly rotated in opposed relationship to eachother about the Hall effect element 12, the sinusoidal output voltagerepresented in FIG. 2 is typically obtained. It has been found that adeviation of less than 2% linearity is obtained when θ is limited to−30°≦θ≦+30°. Although a linear output Hall effect element or transduceris considered to be linear over its span, in practice, no transducer isperfectly linear. The linearity associated with a particular Hall effectelement or transducer such as 2% linearity typically defines the maximumerror which results from assuming the transfer function is a straightline. For the particular sensor output voltage illustrated in FIG. 2,limiting θto the range −30°≦θ≦+30° is beneficial because the linearityof the output voltage over this range is quite good. For applicationswhich require a pulse width modulation (PWM) output signal, the PWMoutput for this range of θ travel is also required. For a PWM outputsignal having a duty cycle range of 10% to 90%, typically the followingcorrelation between the angle θ, the Hall effect element output voltageV and the outputted PWM signal duty cycle is as follows:

Angle θ Hall V(out) PWM (out) −90° 0.5 V — −30° 1.5 V 10% 0° 2.5 V 50%+30° 3.5 V 90% +90° 4.5 V —

To limit the PWM signal to a 90% duty cycle for θ≧30°, a simple voltagedivider may be used. On the other hand, when the magnet orientationangle θ is in the following range,

−30°<θ<0 or 0<θ<90°

a feedback function such as the control circuit 22 illustrated in FIG. 3is typically used to control the PWM output signal. For example, in anapplication where a Hall effect transducer is used to sense the positionof an actuator or to sense a load, it is important to ensure that thePWM output signal is always at the 50% duty cycle when θ=0° for all Halleffect sensors produced for this particular application. Controlcircuitry may accomplish this adjustment by biasing the Hall effectoutput voltage to compensate for any offset.

With respect to the particular sensor application illustrated in FIG. 1,it is important that the null output voltage of the Hall effect element12 remain constant for all sensors and that any misalignment of themagnets 14 and 16 relative to the element 12 at the angle θ=0° will noteffect the null voltage of the element 12 at that position. With the twomagnet arrangement illustrated in FIG. 1, it is important that themagnetic fields generated by such magnets cancel each other out so thatthe overall magnetic field at the sensitive plane 13 of the Hall effectelement 12 is zero. In an application where only one magnet is utilized,the positioning and location of the magnet relative to the sensitiveplane of the Hall effect element must be such that the magnetic fieldgenerated by such magnetic device is parallel to the current directionflowing through the Hall effect element at the angle θ=0° so that againsuch magnetic field has no effect or influence on the sensitive plane ofthe Hall effect element.

In order to avoid additional electronic circuitry to manually adjust ornull the output voltage of the Hall effect element 12 at the zero angleposition, the present magnetic shunt device 18, when properly positionedas illustrated in the embodiment set forth in FIG. 1, will shield andeliminate the affects of the magnetic field on the sensitive plane 13 ofthe Hall effect element 12 at the angle θ=0° to null out any outputvoltage that may be the result of misalignment of the magnetic devicesrelative to the Hall effect element 12.

Although there has been illustrated and described herein a specificembodiment of a Hall effect sensor application 10 incorporating theprinciples of the present invention as illustrated in FIG. 1, it isclearly understood that the sensor embodiment of FIG. 1 is merely forpurposes of illustration only and that changes and modifications may bereadily made to the shape and positioning of the magnetic shunt device18 by those skilled in the art without departing from the spirit andscope of the present invention. Regardless of the application, the shapeand dimensions of the magnetic shunt 18 should be such that the presentdevice 18 shields and nulls the affects of the magnetic field at thesensitive plane of the Hall effect device when the angle between themagnetic field and the direction of current flow through the sensitiveplane of the Hall effect device is substantially zero.

Other aspects, objects and advantages of the present invention can beobtained from a study of the drawings, the disclosure and the appendedclaims.

What is claimed is:
 1. A shunt device for use in a Hall effect sensorhaving a Hall effect element and at least one magnetic device generatinga magnetic field, the Hall effect element having a sensitive planedetecting the magnetic field generated by the at least one magneticdevice, said shunt device being positioned and located adjacent to saidHall effect element and being shaped and dimensioned so as to shield thesensitive plane of the Hall effect element from the magnetic fieldgenerated by the at least one magnetic device when said magnetic fieldis parallel to the sensitive plane of said Hall effect element.
 2. Theshunt device, as set forth in claim 1, wherein the at least one magneticdevice generating a magnetic field includes an electromagnetic device.3. The shunt device, as set forth in claim 1, wherein the at least onemagnetic device generating a magnetic field includes at least onemagnet.
 4. The shunt device, as set forth in claim 1, wherein the atleast one magnetic device generating a magnetic field includes a pair ofmagnets positioned and located in opposed relationship to each other. 5.The shunt device, as set forth in claim 1, wherein the magnetic fieldgenerated by the at least one magnetic device is angularly rotatableabout the sensitive plane of the Hall effect element between an angle of0° wherein the magnetic field is parallel to the sensitive plane of theHall effect element, and an angle of at least !90° wherein the magneticfield is perpendicular to the sensitive plane of the Hall effectelement, said shunt device shielding the sensitive plane of the Halleffect element from the affects of the magnetic field when said magneticfield is located at the 0° angular orientation, and said shunt deviceexposing the sensitive plane of the Hall effect element to the affectsof the magnetic field when said magnetic field is located at someangular orientation other than 0°.
 6. The shunt device, as set forth inclaim 5, wherein the magnetic field generated by the at least onemagnetic device is further angularly rotatable about the sensitive planeof the Hall effect element between an angle of !90° wherein the magneticfield is perpendicular to the sensitive plane of the Hall effectelement, and an angle of !180° wherein the magnetic field is againparallel to the sensitive plane of the Hall effect element, said shuntdevice shielding the sensitive plane of the Hall effect element from theaffects of the magnetic field when said magnetic field is located at the!180° angular orientation, said shunt device exposing the sensitiveplane of the Hall effect element to the affects of the magnetic fieldwhen said magnetic field is located at some angular orientation otherthan 0° and other than !180°.
 7. The shunt device, as set forth in claim5, wherein said shunt device nulls the magnetic field due to anymisalignment of the Hall effect element and the at least one magneticdevice at the 0° orientation.
 8. The shunt device, as set forth in claim5, wherein said shunt device nulls the magnetic field due to anymisalignment of the Hall effect element and the at least one magneticdevice at the ±180° orientation.
 9. The shunt device, as set forth inclaim 1, wherein at least the width of that portion of the shunt devicepositioned to shield the sensitive plane of the Hall effect element fromthe affects of the magnetic field when the magnetic field is parallel tosaid sensitive plane is greater than the width of the Hall effectelement located adjacent thereto.
 10. The shunt device, as set forth inclaim 1, wherein at least the width of that portion of the shunt devicepositioned to shield the sensitive plane of the Hall effect element fromthe effects of the magnetic field when the magnetic field is parallel tosaid sensitive plane is less than or equal to the width of the at leastone magnetic device.
 11. The shunt device, as set forth in claim 1,wherein the width of said shunt device is greater than the width of theHall effect element but less than the width of the at least one magneticdevice.
 12. The shunt device, as set forth in claim 1, wherein saidshunt device is made of a magnetic material.
 13. A magnetic shunt devicefor use in a Hall effect sensor wherein the Hall effect sensor includesa Hall effect element and a pair of magnetic devices, the magneticdevices being positioned in opposed relationship to each other andgenerating a magnetic field, the Hall effect element being positionedand located between the pair of opposed magnetic devices and having asensitive plane which is affected by the magnetic field generated bysaid magnetic devices, said pair of magnetic devices being rotatableabout the Hall effect element between a first position wherein themagnetic field generated by said magnetic devices is parallel to thesensitive plane of the Hall effect element, and a second positionangularly related thereto, said shunt device being positioned andlocated so as to null the affect of the magnetic field on the sensitiveplane of the Hall effect element when the magnetic devices are locatedat their first position, and said shunt device exposing the sensitiveplane of the Hall effect element to the affects of the magnetic fieldwhen the magnetic devices are located at their second position.
 14. Amagnetic shunt device for use in a Hall effect sensor wherein the Halleffect sensor includes a Hall effect transducer and a pair of magneticdevices, said pair of magnetic devices being positioned in opposedrelationship to each other and each generating a magnetic field, theHall effect transducer being positioned and located between said opposedpair of magnetic devices and having a sensitive plane which isinfluenced by the magnetic field generated by said pair of magneticdevices, said pair of magnetic devices being rotatable about the Halleffect transducer in the range of −90 °[[90° where is the angle betweenthe magnetic field generate by said pair of magnetic devices and thedirection of current flow through the Hall effect transducer, saidmagnetic shunt device shielding the sensitive plane of the Hall effecttransducer from the influence of the magnetic field when =0° andexposing the sensitive plane of the Hall effect transducer to theinfluence of the magnetic field when 0 <[90° and when −90°[<0.
 15. Amagnetic shunt device for use in a Hall effect sensor wherein the Halleffect sensor includes a Hall effect transducer and a pair of magneticdevices, said pair of magnetic devices being positioned in opposedrelationship to each other and each generating a magnetic field, theHall effect transducer being positioned and located between said opposedpair of magnetic devices and having a sensitive plane which isinfluenced by the magnetic field generated by said pair of magneticdevices, said pair of magnetic devices being rotatable about the Halleffect transducer in the range of −180 °[[180 °0 where is the anglebetween the magnetic field generate by said pair of magnetic devices andthe direction of current flow through the Hall effect transducer, saidmagnetic shunt device shielding the sensitive plane of the Hall effecttransducer from the influences of the magnetic field when =0° and when=!180°, and said magnetic shunt device exposing the sensitive plane ofthe Hall effect transducer to the influence of the magnetic field when0<[180° and when−180°[<0.